Plasticizing rubber



Patented Sept. 2, 1952 fMaynard Terrence, iwoodsgtown ffij. asstg npi 0 Drawing. I Application December v S r al-No. 131.963

";.T .his invention ,relates to va process for iplastici'zing rubber; novel plasticizfin'g compositions and theresiiltingiplasticized rubber. ,It is .well .known that rubber Wh n subjected to mechanical working in the presence of air or oxygen; rendered more plastic. The-degree oi plasticizatioiilis' determined to a large extent by the time "and temperature of milling. When milled ,for asuificierit length of time, ,rub'ber become's vervso'ft and at the same time will lose mu'chof itsfability .to vulcanize. In order toreducerthfe'ti'me vo' t milling and 'to prevent thed'eterioia'tinguaction of continued milling, it is commonY-practiee to add to the rubherfduring the rrfilling Ioperation, certain -materials-which assist in pr oiiucing a more 'plastic --and workable product'." Materials whichhave been commonly used are. s,l'e'sters, waxes, fats; alcohols, acids,-

are mineralOiljpine'tanpalm 011,;65111 oil, di-

h 'ftyl pht a a e a fi w x. i c r e an stear'icgacid. Relatively large amounts of these agentsmusti loe used to produce the desiredlso ftness. The presence ofthese so called {physical softeners? impai s a number of the physical properties of the resulting vulcanizate and for this reason their use is undesirable.

Aromatic mercaptans and aromatic mercaptides of divalent he'avy'metals are now well known as chemical plasticizing agents for natural'eand synthetic rubbers :as disclosed in U. -S. Letters"Patent21364580;12378519 and $2,467,789. Such chemical plasticizing. vagents I soften rubber without requiring :the addition of :harmful swell ing agents and lubricants, such as oils, il-which continue to 1 aiiect the physical vproperties of the rubberafter-vulcanization; 'I-Iowever, such men captans and 'mercaptides are relatively expensive and this has lsomewhattlimited: theirause.

This" inventioni-ha's gas an object to provide organic "compositions, ;-.which, when added in small amounts-tok-rubber during processing, will. not-only'materially -decrease the time necessary fonhreakdownyof thelrubbergbut will also greatly decrease-the overall time necessaryffor the addition of co pou din a e ts. asfurtherobi ci of this invention is to provide organic chemicals tion' are accomplished by providii rubber p tic'izing compositions which are eom Q 1 Q 0-2'to b ut 5M0 parts? o h tiall y neutral ,niutual, o rg anic s ol hydrocarbon,.alcbhol'ofieste'r,orlini v I twofor' more thereof.

n frubb :haae inatie'm s iie ali i'i cant des- T ili ih Ree -o a-s'maH u the nicliel dithiocarbamatawith the"ar6maic" mercaptan or mercaptide so increases the plasticizing action of the mercaptan and mercaptide that it is possible to obtain a greater plasticizing of the rubber with approximately half the amount of mercaptan that would be used in the absence of the nickel dithiocarbamate. Therefore, it is possible to obtain the desired plasticizing eifect on the rubber with materially less amounts of plasticizing agent, particularly mercaptan and mercaptide, resulting in a distinct saving in cost and increasing the usefulness of the aromatic mercaptans and mercaptides.

The aromatic mercaptans and mercaptides may be those known to the art as useful for plasticizing natural and synthetic rubbers and will include aryl mercaptans, aryl polymercaptans and substituted derivatives thereof in which the substituents may be halogen, hydroxyl, nitro, amino, carboxyl, ester and like, groups. .The aromatic groups may be of the benzene, naphthalene, diphenyl and anthracene series. The aromatic mercaptans and mercaptides have the sulfur directly bonded to a ring carbon atom of a benzene ring. It will usually be preferred to employ the aryl mercaptans and mercaptides, the term aryl being used in its commonly accepted sense as meaning an aromatic hydrocarbon radical. By a heavy metal, I mean a metal having a density greater than 4.0. Ordinarily, the heavy metals employed for forming the arc- Inatic mercaptides will be zinc, cadmium, nickel, tin and lead, of which zinc will usuallybe proferred- I The dithiocarbamates must be the nickel dithiocarbamates, as corresponding dithiocarbamate'sof other metals do not have comparable promotingiefiects on the aromatic mercaptans and mercaptides; The nickel dithiocarbamates should be substantially neutral, that is, they should be freeof strongly acidic groups and strongly basic groups. The valences of the nitrogen of the dithiocarbamic acid groups may be satisfied by hydrogen, hydrocarbon radicals or substituted hydrocarbon radicals in which the substituents may be cyclic ethereal oxygen, secondary amino] or'alcoholic hydroxyl groups. The hydrocarbon groups may be alkyl, aryl, olefinic or alicyclic groups. Preferably, both of the valences of the nitrogen will be satisfied by one or more hydro carbon groups, including a divalent hydrocarbon group which forms with the nitrogen a heterocyclic ring. Also, the hydrocarbon group may link together 2 dithiocarbamate groups. In all casesfthe activity of the 'dithiocarbamates for thepurposes of the present invention depends primarily on the presencein the molecule of the nickel atom attached to 2 dithiocarbamic residues, rather than upon the organicgroups attached to the nitrogen.

p The quantities of the mercaptans or mercaptides and the nickel dithiocarbamates, that is,

the proportion of from about 0.005% to about 0.15%. The amount of the nickel dithiocarbamate may be from about 0.0004% to about 0.05% by weight, based on the rubber, and, preferably, from about 0.001% to about 0.02%. The

ratio of aromatic mercaptan or mercaptide to 4 nickel dithiocarbamate may vary from about 0.2 to about 5000 parts of mercaptan or mercaptide to each part of nickel dithiocarbamate and, preferably, from about 5 to about parts of mercaptan or mercaptide to each part of nickel dithiocarbamate; provided that the proportions of each added to the rubber is maintained within the range above set forth.

While the mercaptan or the mercaptide and the nickel dithiocarbamate may be separately added to the rubber, it will usually be preferred to mix them to provide plasticizing compositions to be added to the rubber. Usually, the nickel dithiocarbamate will dissolve inthemercaptan in the desired proportions to provide a stable composition which can be used as such. In other cases, simple mixtures may be used, with or without aninert solid diluent. The solid diluent may be any filler or pigment for rubber, such as clay, whiting, carbon black, talc, silica, barytes and the like. The amount of solid diluent may be any amount up to that which it is desired to *havein the final rubber composition. Ordinarutes.

. ily, it will be desirable to dissolve the required proportions of mercaptan or mercaptide and nickel dithiocarbamate in a substantially neutral mutual organic solvent so as to contain the plasticizing mixture in a concentration of from about, 10% to about by weight in the solvent. Suitable solvents are hydrocarbons, alcohols andesters which may be aromatic, aliphatic or cycloaliphatic. Preferably, the solvent is one which is volatile under; the processingconditions to be used or is a substance, such as a lubricating oil, which is commonly used in the compounding of rubber. Mixtures of 2 or more solvents may be employed and, where an aromatic mercaptide is involved, the solvent should include an alcohol. Representative solvents which may beemployed are those disclosed in us. Patents 2,064,580, 2,378,519, 2,467,789, hereinbeforereferred to, and in U. S. Patent 2,413,531.

The plasticizing agents and compositions will be incorporated in the raw rubber during the conventional peptizing andplasticizing processes.

ticizing process should be carried out at a tem perature of from about 'C. to about 200 C. In order to more clearly illustrate my invention, preferred modes of carrying the same into effect and the advantageous results to be obtained thereby, given:

the following examples are EXAMPLE I 30 parts of smoked sheet rubber were placed on a small (6" x 2") rubber mill and masticated for 3 minutes at C. The agents to be tested were then added in the quantity (per cent by weight) indicated in the following Tables 1 and 2 and mixed with the rubber at 135 C. for 12 min moved as a sheet and folded. Plasticity pellets were out from a sample of the plasticized polymer and plasticity and recovery measured on a Williams parallel plate plastomer (Williams, Ind.

.Eng; Chem; 16, 362, 1924), following the procedure used in Patent No. 2,467,789. Data obtained, using a mixture of Xylyl mercaptan and nickel dibutyldithiocarbamate as a processing agent for rubber, are recorded in Table 1.

The plasticized rubber so obtained was re-:

EXAMPLE IV and recovery meeeflred on a Williams parallel The peptizing agents of this invention are ef- F71 5113mm plastqmeifeg knowing-the m-oqe-dpxe used in Iective over a rather wide temperature r'a'fie. Combinations of xylyl mercaptan and nickel di- Eizample I.- Data obtained, using a-mixture ef- -niekel dibutyldithiocarbamate and zinc gylyl butyldithiocarbamate were compounded 7, withm fillerc ptide as aprpcesging agent for rubber, are

smoked sheet rubber and tested using the pro- WiliZianie plasticity-recovery measurements recordedin Table 6,

TABLE 6 7 Perr Per-' Mercapttde cent Promoter cent P R 1. .Used, Used- None None .182 60- Zinc xylyl Mercep de 0.10 115 7.. w e Nickeldibutyldithiocarbamate 156v 20 'Zinc Xy1y1-'-Mercept1de- The mror amo listed in Table 6 riowsfth'ic ke .q b w ditm mb me 1. j 'r t n promoter fer z1ne xy1y1 'mercaptide and its use; v

Williams'r plasticity-recovery meagureme nts Temp. Percent 1 Percent Aromatie Thiol Used Prcrnoter Use hgiltljing P B Xylyl Mercaptan 0.03 r, Nene 105 120 4 Do ,ef Nickeldibutyldithmcatbamate; 0 01 105 98 5 7 Do. 'do 0.03 105 86 2 EXAMPLE v parts of smoked sheet. rubber were biased en a,

a small (6" x 2") rubber'mill and masticate d for 3 minutes at 135 C. Thee gents to be tested were then added in the quantity (per cent weight) emall arnounts with the mercaptid'e, makes it possible tevobtai n even greater softening than with 0.10% of the, mercaptide alone. This effect is not limited to zinc xylyl mercaptide but is also shown with other aromatic meraptides as shown in Table 7. V

TABLE 7 Williams plqeticiftZI-Tficqierfl measurements in the rQ'nQWifiQimblsite 1-=e a mm with he Mura 351G-l riizm e 9m h tic ized rubberso obtained'was removed a s 5, sheet and folded. fileticitsi pe llets"were eut from?! sample of the p1aeticized polymer}. 8 p1estic1ty al the me h qu d er ed n Examples -I and Y, eseries of Zinc merca pt ides were evaluated in conjnnctiqn; with nickel butyldithiocarbemate as 'peptizing agents for rubber. The data are summarized in Table 8.

W, H TABLEB,

Williams. plastzcity-recovery measurements Mereaptide 5 Promoter gg P R Zinc-Z-mercapto-benzoie acid 0.10 112 8 methyl ester.

' D0, 0.05 0 Zine-chloropheny1 mercaptide 0.10 119 8 0.705 74 1 0.10 104 4 0.05 78 2 0.10 92 2 0.05 56 1 0.10 174 64 0 0.05 .Niekel dibutyldl 126 8 Zim-maminophenyl mercaptide. 0. 10 113 7 .rDo 0.,05 Nickel dibutyldithiocarbamate- 0.05 4

. :nanhthyl dithiocarbamate; nickel EXAMPLE VII Other nickeldithiocarbamates are also effectiveprom'oters for aromatic mercaptides. Using the testing procedure outlined in Examples I *and' V, a-series of nickeldithiocarbamates were evaluated as promoters for zincxylyl mercaptide. The data-are shown inTable 9.

carbama'te, nickel phenyl ethyl dithiocarbamate and 4-morpholine carbodithioic acid nickel salt.

It will be apparent that, by my invention. the breakdown of rubber can be accomplished more completely and in a shorter period of time with appreciable savings in labor and power consumption, and consequently a much greater output TABLE 9 William's plasticity-recovery measurements .ilmrcavtiae Peg? iNickel Dithiocarbamate 3%? "P; a

v --i 'ione d 172 1'63 Q10 v. N 77135 ::-18 .0. 05 Nickel dimethyldithiocarbamate-. 0. 05 84 2 0. 05 Nickel diethyldithlocarbamate 0. 05 88 I 3 Don im 'd-dai-mtiafi 0.305 N ictkel diisopropyldithiocarbam- 0. 05 179 1 v va e. D.o.,.....- 0. 05 Nickeldibntyldithiocarbamate 0.05 "-62 0 Do. 0105 :4-Morpholinecarbodithioic acid 0.05 =91 5'3 v nickel salt. fiDo,,-........- 0.05 l-Piperidine "carbodlthioic acid 0.05 96 4 nickelsalt. I p .v ;";;D0.'.,...,.'..-.-..-.. .-.,..l;- 0.05 Nlekelphenylethyl dithiocarbam- 0.05 91 3 I a e. v I

4110501111 be understood thatthe preceding ex- .amples1- are ,given for illustrative purposes solely rand that my invention is. not to be limited to --the specific embodimentsdisclosed therein, but '-;,-=that many variations-and modifications may be ;-,made therein without departing .iromthe; spirit or scope of my invention.

..'Examplesof other; aromatic mercaptans that "gzare 'plasticizing-agents'for rubber and may be :.p.- -usedinconjunctionwith nickel dithiocarbamates 4n:- accord with my. invention are thiophenol,

:o-chloro ,thiophenol, dichloro thiophenol, .tri-

,.ch1oro thiophenol, pentachloro thiophenol, nitro .thiophenol, monoand vdi-thio resorcinol, o-amiv.ano thiophenol,.3mercapto benzoic-acid, l-mercaptoxbenzoic acid, thio-a-naphthol, thio-B- c rnaphthol, mercapto 1 anthracene and vmercapto anthraquinone. -Mixtures of isomeric thiols preparedkby treatment of aromatic hydrocarbons, ;-:such -as xylene and naphthalene, with sulfur -.chloride; followed by reduction to 'the thiol are ierred w-i-mercaptides are zinc xylyl' mercaptide, :zcadmium xylylimercaptidaand lead 'xylyl meracaptide.

r-Examples of ,other nickel dithiocarbamates L thaflmaybeused for the purposeof this invention are nickel dithiocarbamataz'nickel;;cycl0- :fhexyl -dithiocarbamate, nickel :dicyclohexyl di- 'lthiocarbamate, nickel 'hexamethylene-bis (di- :thlocarbamate) .anickelsec-butyl dithiocarbam- ;.-ate, {nickel ,phenyl "irnethyl dithiocarbamate, :nickel l-naphthyl-:dithiocarbamate, nickel 2- (Z-hydroxy ethyl) dithiocarbamate, nickel-bis (z-hydroxy eth-yl) dithio'carbamate, and-nickel ethyl dithioacarbamate. ;'I'hei preferred compounds are nickel f fliblltylwdithlOOfiiIbaIflfltG; nickel: dimethyl dithio- "carbamate.

from each piece of rubber equipment. .fIhere is also a savingin cost of plasticizing agent. Furthermore, the plasticizing agents disperse wellin rubben-soiten'the rubber, and also imprQYe. the processing characteristics of the rubber andthe 'ease with which other compounding ingredients are incorporated. Thus; it will be apparent-that -my invention constitutes'a valuable-"advanceand contributionto theart.

I claim: 1. The process for'improvingthe. plasticity of rubber which comprises -.mixing into: therubber from about 0.003% to about 0.5% *of a "rubber plasticizingagent of thegroup consisting'of aroplasticizing aromatic mercaptan .and'fr'om about 1 0.0004% to about 0.05 of asubstantially neutral snickel dithiocarbamate.

3. The process for improving -.the;-plasticity of rubber which comprises mixing-into; the rubber from about 0.003% to about 0.5% 'of-xylyl mer- .captaniancl from"about'0.0004% to about.l0.05'%

of a-substantiallyneutral nickel dithiocarbamate. .4. The process for improving theeplasticityoif rubber which comprises 'mixing'into the rubber from about 0.003%?to about 0.5% of a-"rubber plasticizing aromatic mercaptide of a I? divalent heavy metal and fromabout '0.0004%'=-to' about 0.05% ofa substantially neutral nickel dithio- 5. The. process for'improving thefplasticity of :rubber which "comprises mixing into the rubber from about 0.003% to' about 0.5%:of "zinc" xylyl mercaptidei and from about 0.0004% tot-about 0.05% of a substantiallyneutral nickel idithiocarbamate.

6. Theprocess for improving thezplasticity' of I rubber which comprises mixing into-the 'rubber 'from about 0.003% to about 0.5% of a-r'ubber plasticizing agentof the group consistingpfiaromatic mercaptans and aromatic mercaptideszof divalent heavy metals and from -about.0;0004% to about 0.05 of a neutral nickel .dialkyhdithio- 'carbamate.

7. The process for improving the plasticity of rubber which comprises mixing into the rubber from about 0.003% to about 0.5% of a rubber plasticizing aromatic mercaptan and from about 0.0004% to about 0.05% of a neutral nickel dialkyl dithiocarbamate.

8. The process for improving the plasticity of rubber which comprises mixing into the rubber from about 0.003% to about 0.5% of a rubber plasticizing aromatic mercaptlde of a divalent heavy metal and from about 0.0004% to about 0.5% of a neutral nickel dialkyl dithiocarbamate.

9. A composition, suitable for plasticizing rubber, which comprises essentially from about 0.003 to about 0.5 part of a rubber plasticizing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and from about 0.0004 to about 0.05 part of a substantially neutral nickel dithiocarbamate, which is a strong promoter of the plasticizing action of the plasticizing agent.

10. A composition, suitable for plastlcizing rubber, which comprises essentially from about 0.003 to about 0.5 part of a rubber plasticizing aromatic mercaptan and from about 0.0004 to about 0.05

part of a substantially neutral nickel dithiocarbamate, which is a strong promoter of the plasticizing action of the mercaptan.

11. A composition, suitable for plasticizing rub ber,-which comprises essentially from about 0.003

r to about 0.5 part of Xylyl mercaptan and from about 0.0004 to about 0.05 part of a substantially neutral nickel dithiocarbamate, which is a strong promoter of the plasticizing action of the mer- V captan.

12. A composition, suitable for plasticizing rubber, which comprises essentially from about 0.003

to about 0.5 part of a rubber plasticizing aromatic mercaptide of a divalent heavy metal and from about 0.0004 to about 0.05 part of a substantially neutral nickel dithiocarbamate, which is a strong promoter of the plasticizing action of the mercaptide.

13. A composition, suitable for plasticizing rubber, which comprises essentially from about 0.003 to about 0.5 part of zinc xylyl mercaptide and from about 0.0004 to about 0.05 part of a substantially neutral nickel dithiocarbamate, which is a strong promoter of the plasticizing action of the mercaptide.

'14. A composition, suitable for plastioizing rub ber, which comprises essentially from about 0.003 to about 0.5 part of a rubber plastioizing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and from about 0.0004 to about 0.05 part of a neutral nickel dialkyl dithiocarbamate, which is a strong promoter of the plasticizing action of the plasticizing agent.

15. A composition, suitable for plasticizing rubber, which comprises essentially from about 0.003

. toabout- 0.5 part of a rubber plasticizing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and from about 0.0004 to about 0.05 part of a substantially neutral nickel dithiocarbamate,

which is a strong promoter of the plasticizing action of the plasticizing agent, dissolved in a concentration of from about to about 50% by weight in a substantially neutral mutual organic solvent of at least one member of the class consisting of hydrocarbons, alcohols and esters.

16. A composition, suitable for plasticizing rubber, which comprises essentially from about 0.003 to about 0.5 part of a rubber plasticizing aromatic neutral nickel dithiocarbamate, which is a strong promoter of the plasticizing action of the mercaptan, dissolved in a concentration of from about 10% to about 50% by weight in a substantially neutral mutual organic solvent of at least one member of the class consisting of hydrocarbons, alcohols and esters.

18. A composition, suitable for plasticizlng rubber, which comprises essentially from about 0.003 to about 0.5 part of a rubber plasticizing aromatic mercaptide of a divalent heavy metal and from about 0.0004 to about 0.05 part of a substantially neutral nickel dithiooarbamate, which is a strong promoter of the plasticizing action of the mercaptide, dissolved in a concentration of from about 10% to about 50% by weight in a substantially neutral mutual organic solvent ofat least one member of the class consisting of hydrocarbons, alcohols and esters.

19. A composition, suitable for plasticizing rub ber, which comprises essentially from about 0.003 to about 0.5 part of zinc xylyl mercaptide and from about 0.0004 to about 0.05 part of a substantially neutral nickel dithiocarbamata'which is a strong promoter of the plasticizing action of the mercapticle, dissolved in 'a concentration of from about 10% to about 50% by weight a substantially neutral mutual organic solvent of at least one member of the class consisting of hydrocarbons, alcohols and esters.

20. A composition, suitable for plasticizing rubber, which comprises essentially from about 0.003 to about 0.5 part of a rubber plasticizing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and from about 0.0004 to about 0.05 part of a neutral nickel dialkyl dithiocarbamate, which is a strong promoter of the plasticizing action of the plasticizing agent, dissolved in a concentration of from about 10% to about 50% by weight in a substantially neutral mutual organic solvent of at least one member of the class consisting of hydrocarbons, alcohols and esters.

21. A composition suitable for plasticizing rub ber, which comprises essentially from about 0.003 to about 0.5 part of a rubber plasticizing agent of the group consisting of aromatic mercaptans and aromatic mercaptides of divalent heavy metals and from about 0.0004 to about 0.05 part of neutral nickel dibutyldithiocarbamate, which is a strong promoter of the plasticizing action of the plasticizing agent.

22. A composition'suitable for plasticizing rubber, which comprises essentially from about 01003 to about 0.5 part of xylyl mercaptan and from about 0.0004 to about 0.05 part of neutral nickel dibutyldithiocarbamate, which is a strong promoter of the plasticizing action of the-mercaiptan.

23. A composition suitable for plasticizing rubber, which comprises essentially from about 0.003 to about 0.5 part of zinc Xylyl mercaptideand 13 from about 0.0004 to about 0.05 part of neutral nickel dibutyldithiocarbamate, which is a. strong promoter of the plasticizing action of the mercaptide.

MAYNARD F. 'IORRENCE.

REFERENCES CITED The following references are of record in the 10 file of this patent:

Number Evans Jan. 14, 1947 

1. THE PROCESS FOR IMPROVING THE PLASTICITY OF RUBBER WHICH COMPRISES MIXING INTO THE RUBBER FROM ABOUT 0.003% TO ABOUT 0.5% OF A RUBBER PLASTICIZING AGENT OF THE GROUP CONSISTING OF AROMATIC MERCAPTANS AND AROMATIC MERCAPTIDES OF DIVALENT HEAVY METALS AND FROM ABOUT 0.0004% TO ABOUT 0.5% OF A SUBSTANTIALLY NEUTRAL NICKEL DITHIOCARBAMATE. 